Still no Clovis Comet

I talked once before about the “Clovis Comet” theory, which suggested the widespread extinctions of megafauna in North America at the end of the last ice age was caused by a large comet impact. At the same moment, the highly distinctive “Clovis” archaeological culture was terminated. It was suggested this comet might have either airburst or struck the ice sheets, in either case not causing a visible crater. However, abundant “nanodiamonds”, said to be highly diagnostic of an extraterrestrial impact, were found at a widespread boundary layer roughly associated with the end of Clovis – the start of the Younger Dryas cold period when the earth was suddenly thrust back into near-glacial conditions.

So, I said then and I’ll say again now: this theory didn’t pass the sniff test from the beginning because it is another example of “Clovis exceptionalism” – the skeptical leeway that the Clovis-First model of first peopling of the Americas has been afforded by segments of the archaeological community. No Clovis model was so implausible that it wasn’t given much respectful beard-stroking by the usual silverbacks.

Anyway, subsequent studies of the nanodiamonds and associated evidence have failed utterly to reproduce the findings. Now comes even more news that the comet theory is unsupported and that the original investigators may have mistaken nanodiamonds for, among other things . . . [drumroll] . . . “hardened faecal material from arthropods.”

The [Younger Dryas] impact hypothesis was in trouble already before this latest finding. Many other lines of evidence — including: fullerenes, extraterrestrial forms of helium, purported spikes in radioactivity and iridium, and claims of unique spikes in magnetic meteorite particles — had already been discredited. According to Pinter, “nanodiamonds were the last man standing.” “We should always have a skeptical attitude to new theories and test them thoroughly,” Scott says, “and if the evidence goes against them they should be abandoned.”

But the lead author of two earlier comet-impact papers, Douglas Kennett, an archaeologist at the University of Oregon in Eugene, calls the study “fundamentally flawed science”. “The claim we misidentified diamonds is false, misleading and incorrect,” he adds, although he declined to specify his objections.

And meanwhile, the pro-impact team claims to have found nanodiamonds in the Greenland Ice Sheet, though the date associations are admittedly unclear.

You know, it can be really hard to evaluate these kinds of arguments. What does the average archaeologist know about nanodiamonds? Can we, as outsiders, fairly evaluate competing papers, each of which has been peer reviewed? Perhaps not. So what then? “Argument by Authority” doesn’t really pass muster. And yet, and yet, — when you have a combination of an archaeologist claiming something about nanodiamonds, and someone with advanced training to study nanodiamonds claiming something different, namely that “your nanodiamonds are little tiny balls of shit“, surely that carries some weight.

No offence archaeologists, but almost all of us are jacks of all trades, and masters of none. It goes with the territory. I’m not super comfortable with this decision tree, but added to the original paper being a classic of the Clovis Exceptionalism genre, I’m putting my money on “no comet”. Clovis is still regionally interesting, but it will be understood, as I said previously, on human terms, not extraterrestrial ones.

21 responses to “Still no Clovis Comet”

Awwww – that was a really neat hypothesis. I can bet So how did the original paper get past Science (Nature?) vetting? I bet the Pinter team absolutely roared when they identified the arthropod faeces, they must have known that was a paradigm-breaker! The other side simply couldn’t get their shit together – the possible puns are endless!

Regardless of the cause, the cooling marking the beginning of Younger Dryas does seem to correlate with the end of Clovis. And Clovis really is exceptional in many ways; the lithic technology is extreme and its recognizable over a huge part of the Americas, with no predecessor and an iffy descendant (Folsom).

Morley – the original paper, which is a classic of nominative determinism, being by Firestone et al. – was in PNAS. It passed peer review of course, and I guess the possibility remains it is accurate. There is a good series at John Hawks weblog as well as Anthropology.net, which follow the various rebuttals and reanalyses. I can’t put it all together in my head – like I say, it is hard to sit on the outside and evaluate competing peer reviewed articles in such a niche specialty.

So, the following are all readable and written by non-journalists with no real axes to grind I don’t think. Might be helpful.

A hypothesized extraterrestrial impact in North America at 12,900 calendar years BP (12.9 ka) has been proposed as the cause of Younger Dryas climate changes, terminal Pleistocene mammalian extinctions, and a supposed “termination” of the Clovis archaeological culture. In regard to the latter, however, an examination of archaeological, geochronological, and stratigraphic evidence fails to provide evidence of a demographic collapse of post-Clovis human populations, especially where the Clovis and post-Clovis site records are reasonably well constrained chronologically. Although few Clovis sites contain evidence of an immediate post-Clovis occupation, interpreting that absence as population collapse is problematic because the great majority of Paleoindian sites also lack immediately succeeding occupations. Where multiple occupations do occur, stratigraphic hiatuses between them are readily explained by geomorphic processes. Furthermore, calibrated radiocarbon ages demonstrate continuous occupation across the time of the purported “Younger Dryas event.” And, finally, the relatively few sites purported to provide direct evidence of the 12.9-ka impact are not well constrained to that time. Whether or not the proposed extraterrestrial impact occurred is matter for empirical testing in the geological record. Insofar as concerns the archaeological record, an extraterrestrial impact is an unnecessary solution for an archaeological problem that does not exist.

Hmm, well John I’d say it is actually a pretty fascinating story of competing empirical results, all published in high quality peer reviewed journals. How can this be? What does this tell us of peer-review, if anything? And, how do we, as outsiders, decide who to believe?

The scary thing for me, anyway, is that I lean to the no-comet theory, but fully realize this is because I am predisposed to the Clovis-isn’t-first model of first peopling, and also because I am wary of models which summon forth exceptional characteristics of Clovis. We’ve seen a lot of those come and go, from the Blitzkrieg model with its unusually fecund human killing machines to the Swan Shaman piping his charges through the Quacks in the Ice. But belief in a model is most definitely NOT a means to pick between competing empirical observations and that leaves me uneasy about my predispositions. Good luck with your essay!

Around 300 University Students (SFU) will be/are reading your journal to complete their essays!

In regards to the theories available, I am confused as to what happened to all the mammal bones/remains?

Apparently only 14 sites have been found across North America, but none have indication to be mass killing sites. Maybe the mammoth population was already on a steady decline before hand and coincidently the Clovis people just came at a bad time.

I personally agree on the pre-clovis notion myself. I think many are scared in considering such a model due to all the history and politics that have been based around it. It just seems like a better story for people regarding the past. People have a tendancy to only notice what they want to (further) prove.

1. Never trust anything you read on a blog no matter how well written and witty, but verify, verify, verify anything you read on the internet….

2. For the extinction problem, start with Grayson DK, Meltzer DJ (2003) A requiem for North American overkill. J Arch Sci 30:585–593. Go on Web of Science through the SFU library portal, find this article, and then find more recent articles that cite this one. Also check out the recent paper by Gill et al. I comment on here, which explores mastodon decline pre-Clovis.

Given the size and density of the micrometeorite spherules they are looking at, there aren’t many sedimentary contexts in western NA where these would be readily discerned today. Even in a core from an Alaskan bog, the odds of a chance encounter (or chance identification) of such a small object would be low. Anyways, not arguing for one side or the other of this thread, but if one looks hard enough (from the right angle) they’re bound to find the evidence they want to find …

It pretty much demolishes all the evidence so far put forth – maybe not the tusk evidence. I mean, they are unequivocal that none of the findings can be replicated in the very same samples from the Younger Dryas boundary used in the original study, or if they can be, are not unambiguously the types of evidence strongly associated with extraterrestrial impacts.

Maybe this is the start of a new slugging match but right now the Earth Science folks are winning big time, from my seat a long way from the ring, at least. The tusk stuff is cool though and maybe it will turn the tables back again.

Ever had a sudden ‘ouch’ thinking it was a bug bite ? You may want to start thinking micrometeorite now … get your magnet out and probe your wound 😉 $50 to the first archaeologist who can prove they’ve been penetrated by an extra-terrestrial body

Rémi – I notice you did not challenge us to prove that you have not been penetrated by an extra-terrestrial body? I am sure if we look hard enough, from the right angle, with some judicious subsurface testing we can find extraterrestrials embedded in you, somewhere 🙂

Update 2012: Reports of the debunking of Firestone et all, and demise of the Younger Dryas Impact hypothesis were premature, and vastly over stated. And while the stratigraphic layer containing ET materials at all other sites tested has been thin and difficult to identify, In Mexico, in the sediments of Lake Cuitzeo, the impact layer is a full 10 centimeters thick.

sites common to Firestone et al. and Surovell et al. They reported that “spherule abundances are consistent with those of Firestone et al.” and “inconsistent with the results of Surovell et al.” They also concluded that Surovell et al. altered the prescribed MSp protocol in fatal ways, particularly by not observing requirements

for sample thickness, sample weight, and size sorting. We consider these discrepancies significant enough to negate the conclusions of Surovell et al. Daulton et al. found no YDB NDs at Arlington Canyon, California, or at Murray Springs, Arizona, as earlier reported in Kennett et al. They searched for NDs in “microcharcoal aggregates” from the Murray Springs YDB site and, finding none, claimed to refute the previous results. However, Kennett et al. never claimed to find NDs in charcoal, and instead, observed NDs at Murray Springs in acid-resistant residues from bulk sediment which Daulton et al. did not investigate. Daulton et al. further speculated that Kennett et al. misidentified YDB NDs, observing copper instead, which displays d-spacings nearly identical to n-diamond and i-carbon. In addition, Daulton et al. pointed out that graphene and/or graphane have d-spacings similar to lonsdaleite and that the lonsdaleite diffraction pattern reported from Arlington Canyon by the Kennett et al. was missing the lonsdaleite diffraction line at 1.93 Å. However, in YD-aged ice in Greenland, Kurbatov et al. identified lonsdaleite with the 1.93- Å line, which definitively demonstrates that those Greenland nanoparticles cannot be graphene or graphane. At Lake Cuitzeo, numerous NDs have been identified with the 1.93 Å line, as shown in Fig. 8 Aand B and Fig. 11B, eliminating the possibility that these crystals are graphene or graphane. SAD and all other analyses conclusively show that the Cuitzeo nanoparticles analyzed have d-spacings consistent with lonsdaleite and other NDs. In independent support of NDs in the YDB, Tian et al. and Van Hoesel‡ identified cubic NDs in the YDB layer in Europe.

Regarding CSp, Scott et al. speculated that those found at YDB sites are simply charred fungal sclerotia, which are ball-like clusters of long, branching filamentous structures, common to some fungi. The CSp from Cuitzeo and other YDB sites are unmistakably different from sclerotia in numerous critical characteristics. In particular, charred and uncharred sclerotia have textured, filamentous, low-reflectivity interiors, whereas at Cuitzeo, SEM imaging demonstrates that CSp have smooth, glassy, highly reflective interiors with no evidence of filamentous structure observed in fungal sclerotia (or cellular structure found in charcoal) (SI Appendix, Fig. 5). Cuitzeo CSp also contain numerous noncarbon particles, including aluminosilicates, indicating that these cannot be primary biological entities, such as sclerotia. In support of this, several lines of evidence support the formation of CSp during biomass burning. For example, Firestone et al. reported the production of CSp in modern wildfires, and laboratory experiments have demonstrated the production of CSp from charred tree resin at approximately 500 °C***. These CSp are morphologically identical to those found in the YDB but contain no NDs. Also, CSp similar to those found in the YDB have been reported by Harvey et al., who observed vesicular CSp in the impact layer at the KPg, and suggested that CSp, along with aciniform soot, formed during impact into carbon-rich target rocks.

Ok, that’s a good enough comment, thanks. It would be nice if the blog post author would address the issue of his mistaking the nanodiamonds with balls of shit, since the nanodiamonds are on the order of nanometers, and the authors mistaking the balls of shit for spherules were referring to something that is orders of magnitude larger than the nanodiamonds.